E-liquid or more commonly 'Vape Juice' usually comes in 3 main types with the main differences being the consistancy of the E-liquid or the type of nicotine used. It is Important to choose the right E-liquid type for the vape kit you are using so that the coil is able to function properly, If the liquid is too thick the coil may burn out quickly, too thin and it could leak from the tank.

50/50 E-liquid is the perfect vape juice for starter kits.
Nic salt vape juices will give you a smoother throat hit at high nicotine levels and are popular for Vape Starter kits and Pod Kits.
High Vg Vape Juice is Perfect for high powered Sub Ohm Kits.